Molded airfoil, especially for sustaining rotors



y 19465 A. E. LARSEN 2,400,649

, MOLDED AIRFOIL ESPECIALLY FOR SUSTAINING ROTORS v F iledFeb. 27. 19422 Sheets-Sheet 1 M mm May 21, 1946. A. E. LARSEN MOLDED AIRFOILESPECIALLY FOR SUSTAINING ROTORS 2 Sheets-Sheet 2' Filed Feb. 27,. 1942Patented May- 21, 1946 FFICEV MOLDED AIRFOIL, ESPECIALLY FOR SUSTAININGROTORS Agnew E. Larsen, Jenkintown, Pa., assignor to Autoglro Company ofAmerica, Philadelphia, Pa., a corporation of Delaware ApplicationFebruary 27, 1942, Serial No. 432,544

2 Claims.

This invention relates to molded airfoils. While some of the broaderaspects of the invention are applicable to airfoils generally, theinvention is particularly concerned with rotative airfoils, and moreespecially with the blades of aircraft sustaining rotors. Sustainingrotor blades are customaril of considerable length and, therefore, giverise to special problems of struc ture and operationresulting, forinstance, from the high centrifugal forces set up in operation.

One of the primary objects of the invention is the provision of a bladewhich may readily and economically be molded, rather than built up'ofmany pieces, ashas been customary in the practice of the'prior art. Ingeneral, according to the-preferred practice of the present invention,the blade is composed of two portions, one portion constituting alongitudinal strength structure having blade mounting means associatedtherewith, and the other constituting the molded material which ismounted on and secured to the strength structure and defines the airfoilcontour of the blade.

Special features of construction of both of the major parts of the bladeare provided for in accordance with the present invention, in order tomeet a variety of different problems and requirements, all as will morefully appear hereinafter.

More specifically, it may be pointed out that the invention has in viewmaking possible and practicable the molding of rotor blades fromcellular, and preferably resilient, material of the general nature ofexpanded" or sponge rubber;

Many such materials, having varying degrees of the normal flexing anddeformation of the blade which occurs in operation.

By the employment of molded cellular mate rial, lightweight constructionis secured, and the total quantity of material used is kept at aminimum. How the foregoing and other objects and advantages are attainedwill appear more fully from the following description, referring to theaccompanying drawings, in which- Figure 1 is a fragmentary perspectiveview of a blade constructed in accordance with this invention and moreparticularly illustrating the blade section:

Figure 2 is a plan view, on a reduced scale, of a part of the blade ofFigure 1, the central portion and tip of the blade being broken away;

Figure 3 is a view similar to Figure 1 but illustrating a modifiedblade;

Figure 4 is a view similar to Figure 2 illustrat ing the construction ofFigure 3;

Figure 5 is a fragmentary plan view of still another form of blade, withintermediate and tip portions broken away; I

Figure 6 is a fragmentary sectional view, on an enlarged scale, taken asindicated by the line 6-6 on Figure 5; I

Figure 7 is a view similar to Figure 1 but taken generally as indicatedby the line on'Figure 6; and

Figure 8 is a detail view of one part employed in the form illustratedin Figures 5 to '7.

In connection with Figures 2, 4 and 5, it may be mentioned that thebreak in each of these views represents the omission of the majorportion of the blade length since, in most instances, sustaining rotorblades have a length of the order of twelve to fifteen times the chorddimension,

The blade of Figures 1 and 2 comprises a longitudinal strength structuretaking the form of a tubular metallic spar 9 extended preferablysubstantially throughout the entire length of the blade. At the innerend of the spar a fitting I0 is provided, having an apertured lug I I bymeans of which the blade may be pivotally connected to a rotative hub.Preferably, the blade mounting includes at least a flapping pivotproviding freedom for movement of the blade transverse its mean rotativepath of travel, and also a drag pivot (which may cooperate with lug ll)providing freedom for movement of the blade fore and aft within itsgeneral path of rotation. Since,

such pivots form no part of the present invention per se, only briefreference is made thereto.

The blade is preferably built up by initially forming upper and lowerblade sections l2 and I3, adapted to interflt at mating surfaces lyinggenerally in the mean plane of the blade. Each section is molded ofcellular material and is provided with an elongated groove or recessadaptedto fit the spar 9. When assembled, the two sections preferablydefine .the complete airfoil contour of the blade, the sections beingjoined at the junction line I4 in the manner described more fullyhereinafter,

It may be noted that Figure 2 illustrates the spar 9 as laid in the sparrecess of the lower section l3 of the blade.

As will be observed from inspection of Figure l, the outer surface layerl5 of the molded cellucome very close to the spar 9. This is proofingdope or paint. Alternatively, be applied to the surface in a mannerdiscussed spar, I prefer to employ.

exterior metal surface of two sections of the blade, or

Y highly advantageous from the In, this form of construction,

than interior portions of the blade, this denser layer being indicatedby heavier stippling. Similarly, a denser layer l6 occurs'immediatelyadjacent to the spar 9, and in the preferred practice these dense layersl5 and I6 merge, or at least. each other, *above and below ofadvantage-in contributing to the strength of the cellular moldedmaterial.

A dense section II is also provided at the nose is of the blade, andanother similar section I 8 at the trailing edge, these dense nose andtrailing edge regions acting somewhat in the manner of nose and trailingedge stringers for stiffening and I reinforcing the blade. The noseregion I the further object and advantage of mainta g thesectionalpenter of gravity of the blade well forward, which is ofimportance for aerodynamic reasons which need not be considered herein.

. or partial ribs spar are provided with flanges a projecting rearwardlytherefrom 'a greater distance than in Figure 2, each of these flanges20a desirably projecting part-way into a bulkhead 23 for reinforcementthereof.

Ports 25 in the bulkheads serve to interconnect carried by the theseveral cavities 24, and provision is made for has 15' venting thesespaces, as through a vent 26, located adjacent the tip of the blade.Undesired buildup of pressure within the cavities 24 toward the.outboard end of the blade under the action of centrifugal force isthereby avoided.

,The blade structure of Figures 5 tot! inclusive is also built up on alongitudinal strength struc-- ture, taking the form of spar 21 of thegeneral type shown in patent of Paul H. Stanley and Agnew E. Larsen, No.

- 2,272,439 granted February 10, 1942.

In accordance with the preferred practice, all 20 of the dense portionsof the cellular molded material (I5, l6, l1 and iii) are provided bycuring or heat treatment, such as vulcanizing,'this heat treatmentprocess being effected in a manner to at least partially eliminate thevoids in face layers and in the nose and trailing edge strips. In thisway, not only the strength ofv the blade is enhanced but, in addition, asmooth exterior surface is provided. The surface may be finished byapplication of suitable weatherfabric may hereinafter in connection withthe third form of blade disclosed.

With reference to the attachment of the mold- 'ed sections I2 and 13 toeach other and to the brass .or copper plated. Similarly, the twosections oftlie blade may be directlyvulcanized to each other at theirmating surfaces.

Bonding may also be achieved by the use of adhesives, either at themating surfaces of the at the spar, or both.

In any event, the bonding of the molded matethe sur- 5 One of theprimary differences between the blade here shown and those previouslydescribed is that the blade is molded in sections adapted to be arrangedin a series lengthwise of the blade, each section defining the fullcross sectional contour of the blade. Figure 6 illustrates portions ofblade sections 28 and 30,and also the intermediate section 29 in full,and from examination of this bonding for this pur- With vulcanizablematerials, the blade sec- I blade accordance with the description ofFigures 1 to 4 rial to the spar throughout the length thereof isstandpoint of transmitting the centrifugal loads from the moldedmaterial to the spar and from there through the root end mounting to therotor hub.

Thebonding may also serve to secure the molded material to the spar intorsion.

If desired, collars l9, having flanges or-partial ribs2ll, may besecured to the spar at spaced intervals, as indicated in Figure 2, andfitted or ther enhance the keying of the blade proper to the spar,

view it will be seen that each section is provided with an aperture theseveral sections being serially threaded onto the spar. I p

A further characteristic of the blade of Figures 5 to 8 is the fact thatoutboard sections of the blade are of corresponding spar 21. As shown inFigure 5, the plan form-of the blade as a whole may also betaperedtoward the blade.

that each section of the be molded of material in the outboard end of Itis contemplated here shown shall inclusive, althoughthese sections aredesirably molded as units, rather than formed of upper and lower matinghalves.

In building up the inboard end section is spar from the outer end 3| isthreaded onto the spar tion so as to transmit force from the inboardmolded section to the spar. This procedure followed for each successivesection of the blade, working outwardly toward the tip. The rib 3| isprovided with a flange 32 or other suitable means forwelding or otherattaclnnent to the spar.

When all sections of the blade are assembled on the spar, junctionstrips 33, forinstance of rubberized fabric, may be. applied to join thefirst threaded onto the thereof, after which a rib and secured inposimating surfaces of adjacent sections and proembedded in the moldedcellular material to fur- Many features of the arrangement of Figures 3and 4 are similar to thosedescribed above. Here, however, the ellipticaltube 2| and each of the blade sections l2a and He is provided with aseries of recesses 22 .to the rear of the spar, the recesses beingseparated .by bulkheads 23. The recesses and bulkspar takes'the form ofan 05 in combination with heads of each blade section are located so asto register when the two sections are brought together, thereby forminga series of cavities such as indicated at 24 in Figure 3, for lighteningthe trailing edge portion of the blade. 7

the collars I M.

vide a smooth exterior surface. Following this, a fabric covering 34 maybe applied and doped in place.. In applying the fabric covering (which,

as before indicated, may also be used in the blades of Figures 1 to 4inclusive) adhesive or dope may be relied upon for securing the fabricin place molded material. It maybe mentioned that this expedient may beemployed as an alternative or the surface layer of increased density, inorder to provide the desired strength-.- ening, reinforcement andsurface.

While the ribs i l 'in the arrangement ofFigtires 5 to 8 may be themeans relied upon for transmission of the centrifugal load from the anelliptical step-tapered adapted to receive the spar 21,

thickness,v somewhat to the taper steps of the blade of Figures 5 to a,the

the load of centrifugal if desired, heat may be applied so as to embedthe fabric directly in the surface layer of the smoothness of the bladeblade sections to the spar, even in this form the blade sections arealso preferably bonded directly to the spar, as described above.

A ballast rod 35 may be threaded into apertures provided toward the noseof the blade sec- 1 tions for the purpose -of maintaining the crosssectional center of gravity well forward.

I claim: 1. An aircraft sustaining rotor blade comprising a mainlongitudinally-extending metallic spar; a plurality of retaining membersfixedly located on said spar at intervals along its length; a pluralityof blade body members of molded homogeneous material, said body membershaving cavities abaft the spar and bulkheads separating the cavities,and said body members further being preformed to receive the spar, toengage the retaining members within the bulkheads, and to matei'nabutting relationship; and an external covering of sheet material, saidblade body members being mounted on said spar in abutting relationshipand being secured by bonding as against ,relative movement of onemember'with respect to another, and being secured asa ainst displacementlengthwise of the spar by said retaining elements, and being, furthersecured as against disruptive forces, by being bonded to said sheetmaterial in the region of the joints between abutting body members, saidretaining members serving also as stiffening members for the blade thecavities aforesaid.

as a whole. and for the bulkheads lyingbetween I 2. An aircraftsustaining rotor blade comprising preformed to receive the spar, toengage the retaining members within the bulkheads, and to mate inabutting relationship, and an external Q covering of sheet material,said blade body memhere being mounted on said spar in abuttingrelationship and being secured by bonding as against relative movementof one member with respect to another, and being secured as againstdisplacement lengthwise of the spar by said retaining elements, andbeing further secured asagainst disruptive forces, by being bonded tosaid sheet materlal in the regionof the joints between abutting bodymembers, said retaining members serving also as stiflening members forthe blade as a whole, and for the bulkheadsdying between the I cavitiesaforesaid, in which structure means are provided for-venting adjacentcavities lengthwise of the blade and for venting the outermost" cavityto the atmosphere.

AGNEW E; LARSEN.

